The conversion of ethers to the corresponding alkenes and alcohols, preferably alkanols, i.e., aliphatic alcohols, is an important reaction in a number of commercial processes. Thus, for example, this reaction is used to remove ethers, such as isopropyl ether, produced as the by-products of olefin hydration processes, such as the hydration of propylene to produce isopropanol.
Various catalysts have been proposed for the decomposition of ethers, for instance, in U.S. Pat. Nos. 4,691,073; 4,254,290; 4,320,232; 4,521,638; 4,398,051; 4,357,147. “Production D'Isobutene de Haute Pureté par Décomposition du MTBE” by P. B. Meunier et al. in Revue de L'Institut Francais du Petrole, vol. 46, No. 3, May 1991, pages 361 to 387, U.S. Pat. Nos. 5,254,785, 5,177,301, 5,117,920 and Japanese Published Patent Application No. JP-A-06072904.
U.S. Pat. No. 4,352,945 describes discloses a process for producing isopropanol comprising (a) contacting water and a feedstock comprising propylene with a catalyst comprising an acid ion exchange resin in a first reaction zone under hydration conditions to produce a first stream; (b) dividing the first stream into a second stream comprising water and isopropanol and a third stream comprising diisopropyl ether; (c) contacting the third stream with a reversion catalyst in a second reaction zone under reversion conditions to produce a fourth stream; (d) separating propylene from the fourth stream; (e) recycling the propylene to step (a); and (f) recovering isopropanol from the second stream. The reversion reaction uses a silica alumina cogel catalyst.
U.S. Pat. No. 4,357,147 describes a process for producing an oxygenated fuel blending composition comprising (a) contacting water and a feedstock comprising propylene with a catalyst comprising an acid ion exchange resin in a first reaction zone under hydration conditions to produce a first stream; (b) dividing the first stream into a second stream comprising water and isopropanol and a third stream comprising diisopropyl ether; (c) contacting the third stream with a reversion catalyst in a second reaction zone under reversion conditions to produce a fourth stream; (d) separating propylene from the fourth stream; (e) oligomerizing the propylene; and (f) recovering isopropanol from the second stream and blending it with a gasoline blending hydrocarbon stream. The reversion reaction uses a silica alumina cogel catalyst.
Strategies to minimize the production of isopropyl ether (IPE) in processes for the manufacture of isopropanol include 1) running a low propylene conversion process, 2) recycling the IPE back to the reaction zone, 3) decomposing the IPE to propylene using acid catalyst, or 4) hydrolyzing the IPE to isopropyl alcohol (IPA).
However, low conversion processes create large recycle streams requiring large reactors, large amounts of catalyst, and fractionation of reactor effluent to create a highly concentrated propane stream for purging. If dilute propylene is used then a purification step is required for the propylene return stream.
Recycling the IPE back to the hydration unit is feasible because the reaction of IPE to IPA and/or propylene can be equilibrium controlled and is reversible in the hydration zone. Recycling IPE permits recovery of IPA and/or propylene from the IPE, but it does not eliminate the formation of IPE. In some cases it is not possible to recycle all of the IPE back into the feed and therefore other dispositions for the IPE must be found. Additionally, recycling IPE to the front end decreases the capacity of the unit by the amount of IPE recycled.
Thermal decomposition of ethers typically occurs at elevated temperature (typically >350° C.) and generates significant thermal side reactions that create impurities that must be removed before recycling. The recycled impurities quickly build up to unmanageable levels if the propylene is not purified.
The hydrolysis of IPE to produce IPA typically occurs at higher pressure, in the presence of an acidic catalyst, and requires significant amounts of water in the feed, which results in a need for large equipment and large water removal capability. The hydrolysis step can become hydraulically limiting if the water/IPA stream is returned to an existing unit.
Unpublished International Application No. PCT/US2004/041546 discloses a process for selectively converting a dialkyl ether to the corresponding alkene and alkanol, the process comprising contacting a feed containing at least one dialkyl ether with a catalyst comprising an acidic mixed metal oxide having the following composition:XmYnZpOqwhere X is at least one metal selected from Group 4 of the Periodic Table of Elements, Y is at least one metal selected from Group 3 (including the Lanthanides and Actinides) and Group 6 of the Periodic Table of Elements and Z is at least one metal selected from Groups 7, 8, and 11 of the Periodic Table of Elements; m, n, p and q are the atomic ratios of their respective components and, when m is 1, n is from 0.01 to 0.75, p is from 0 to 0.1, and q is the number of oxygen atoms necessary to satisfy the valence of the other components. The mixed oxides preferably contain sulfur, typically present in an amount of up to 5 wt %, such as up to 1 wt %, of the final mixed oxide composition. The mixed oxides can prepared by impregnation or by co-precipitation from a liquid mixture containing a source of Group 4 metal ions and a source of Group 3 and/or Group 6 metal ions. These catalysts exhibit both high selectivity and long catalyst lifetime when used as ether decomposition catalysts.
The ether decomposition process integrated into a commercial alcohol process, for example IPA, of the present invention enables high selectivity in the conversion of propylene to IPA and provides high purity propylene in the recycle stream.